In PrEP studies, people who are at high risk of HIV but are HIV negative take anti-retroviral medication daily to try to lower their chances of becoming infected with HIV if they are exposed.

The CDC's Morbidity and Mortality Weekly Report, released Thursday, said the National Institutes of Health announced trial results in November providing the first evidence that daily oral use of an anti-retroviral drug used to treat HIV can also help prevent sexually-acquired HIV among men who have sex with men, when delivered as a part of comprehensive HIV prevention services.

Until detailed guidelines are available, CDC is providing interim guidance.

"The CDC underscores the importance of targeting PrEP to men who have sex with men at high-risk for HIV is a part of comprehensive HIV prevention services, which should include risk-reduction and medication adherence counseling, condoms and testing and treatment for other sexually-transmitted infections", the report said. "The guidance stresses the need to ensure any men who have sex with men who may be prescribed PrEP are confirmed to be HIV negative prior to use, as well as the need for regular monitoring of HIV status, side effects, adherence and risk behavior among those taking PrEP."